Not knowing how you've got things setup, but if all the xbox needs is internet access, then surely you can just get an adsl router, bang in your username and password, and presto, internet on both machines without having to install AO(hel)L software on the XBox.....
I set this up for a couple of people at work the other week - they thought they had to install the AOL software on both machines that were connected to the internet, but that actually wasn't the case, and both would talk to the internet using AOL as the ISP quite happily.
Of course, I may have completely mis-understood the above, in which case, just ignore the post
-Alex